The present invention relates to a sewing apparatus capable of producing a seam along a three-dimensional bent curve.
There are known devices wherein the needle system is mechanically coupled to the looper system and is movable along two coordinate axes, i.e., in the plane of the material to be sewn. Such sewing devices operate successfully for planar workpieces.
However, there are numerous products having seams, wherein the seam, in the finished product, forms a curve in space. Furthermore, in products which consist of several and/or thicker layers of material sewn together, there arises the problem that, although it might be possible to sew the layers together in a planar condition, wrinkles are produced on the inner side of the curvature when bending the multi-layered structure thus produced, while a considerable stress is put on the material and especially on the seam at the outer side of the curvature by the resulting tension. Therefore, there has been the need to sew the layers of such products together in a condition which corresponds to the shape of the finished product.
A sewing machine is known from the European lay-open print 0 107 910, wherein the needle system and the looper system are arranged on an essentially vertical carrier in such a way that they are movable relative to one another in the direction of the needle axis, and that they can be rotated about the needle axis into four positions spaced apart from one another by angles of 90.degree.. The carrier itself is translationally movable along a horizontal coordinate axis and is pivotable about this axis about a limited angle of 15.degree.. The workpiece is clamped in a support by means of which it is translationally movable along the second horizontal coordinate axis, as well as rotatable about said axis. This allows to sew seams in a cylindrically curved workpiece parallel to the cylinder axis and in the circumferential direction of the workpiece. Because of the mechanical limitations, this device is not suited for sewing along freely selectable three-dimensional spatial curves. Furthermore, the arrangement does not allow to produce seams in hollow bodies.
U.S. Pat. No. 3,515,080 describes a sewing device, wherein the needle system and the looper system are translationally movable along all three coordinate axes and rotatable about said axes, wherein the needle system and the looper system are drivable mechanically independent of one another and are merely interconnected via an electronic circuit. The embodiment shown in the above-mentioned patent shows a sewing device wherein the needle system and the looper system are movable along two horizontal coordinate axes and are rotatable about the third coordinate axis. This only allows to produce seams in a horizontal plane. The above-mentioned patent does not disclose how the needle system and the looper system are to be arranged for being translationally movable along all three coordinate axes and for being rotatable about these coordinate axes, which would allow to produce a seam along a three-dimensionally bent curve.